Vibration absorbing structures for heavy construction purposes

Details Vibration absorbing structures for heavy construction purposes Vibration absorbing structures for heavy construction purposes

1993-10-19

1995-01-31

Butler, Douglas C.

Brakes

Inertia of damping mass dissipates motion

267136, 14 25, F16F 710, E01D 1512

Patent

active

053852192

DESCRIPTION:

BRIEF SUMMARY
This invention relates to structures for heavy construction purposes, adapted to function when in a stable erected state and including a first structural element and a second structural element juxtaposed to each other and adapted for direct transfer of structural loads between them when the structure is in the erected state.
The term "structure", as used herein and as qualified above, is to be taken to mean a structure which, when not in a stable erected state, is in a structurally deficient state, that is to say a state in which it is neither statically determinate nor redundant. Such a state is sometimes referred to as "unstable".
Such structures may take many different forms, notably that of a frame type construction, for example a frame of a building, a support frame for heavy chemical plant, a bridge, and so on. As used herein, the term "structure for heavy construction purposes" embraces any structure which is itself "heavy" and which is either the object of construction itself (for example a bridge or a building frame), or is a structure used during construction of something else. Examples of this latter type of structure include cranes, tunnelling equipment, certain types of earth moving and excavation equipment, launching rails for temporary bridges, etc. Structures of this type may indeed be used for purposes which are not strictly "construction", and an example of these might be a walking dragline or similar used in opencast mining.
"Heavy construction Purposes" is therefore to be construed in a correspondingly broad way. In general, the invention is concerned with what happens when the structure in question is not in its stable erected state but is itself structurally deficient, for example (and especially) while it is being erected. In particular, the invention is concerned with the damping of forced vibrations, especially (though not necessarily) those which arise when one member of the structure is cantilevered or otherwise liable to undergo vibration in its natural flexural mode. Thus, in the above definition, the first element of the structure may, during the course of erection, undergo very low frequency flexural vibration which, in the case of a long and heavy member, can under some circumstances make it at least dangerous and sometimes unmanageable. This may occur as a result of applied forces, e.g. due to the action of wind, or may occur naturally as a result of vortex shedding when the member is being moved through the atmosphere.
The use of what will be called a dynamic absorber for damping vibrations in a body has been known per se for a long time. A dynamic absorber, as proposed up to the present time, consists essentially of a mass which is provided especially for the purpose and which is attached to the body to be damped by means of a spring or other resilient element. The stiffness of the latter, and the magnitude of the mass, are so chosen that when the body to be damped is subjected to influences such as to cause it to vibrate, these vibrations are absorbed by the dynamic absorber, which then itself undergoes oscillations. Depending on the extent to which the dynamic absorber is accurately tuned to the particular frequency or frequencies of the vibrations actually being damped, the amplitude of vibration of the main body is reduced by a greater or lesser amount, and may sometimes be eliminated altogether.
Practical applications of dynamic absorbers, sometimes called dynamic eradicators, dynamic balancers or inertia dampers, include a number of published proposals for use as part of vehicle suspension systems, or for use in preventing vibration occurring in scientific instruments. It has also been proposed to use a pendulum, attached by means of an elastic element to a civil engineering structure, for example a tall lattice tower, the pendulum having an appropriate mass and acting as an indicator that forces are acting on the structure such as to cause it to vibrate, while the absorber of which it is part reduces or eliminates that vibration.
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REFERENCES:
patent: 3490605 (1970-01-01), Ross
patent: 4470121 (1984-09-01), Ebert
patent: 4924976 (1990-05-01), Bernett
patent: 4972538 (1990-11-01), Parramore

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